1. Field of the Invention
This invention relates to a power supply circuit for a diode adapted to emit light in dependance of the prevailing surrounding light.
2. Description of the Prior Art
It is previously known to design a power supply for a diode comprising a power source and first and second transistors arranged in darlington connection, the base of the first transistor being connected to the power source via a photo cell, the emitter of the second transistor being connected to said diode.
A power supply of this type has been used for a diode applied as an aimpoint in an optical aiming device. This is described in the unpublished Swedish Application No. 7809676-5. Also, U.S. Pat. No. 3,833,799--N. A. Audet--Sept. 3, 1974 is related prior art.
3. Object of the Invention
Although such known circuit fulfills very high requirements regarding adapting the power supply in dependance of the prevailing surrounding light it has been desirable to provide a circuit having an operating range offering between 100 and 1000 times more variation in power than has been possible with the known power supply circuit.